I think there may be some kind of authentication involved.
Make sure to have your Xbox Controller S plugged to your Pi before starting GIMX.
Please make a log file with adapter debug messages enabled, and let me know the result.

Hi,
Still no reaction on console either with DS4 or Xbox Controller S but maybe the log can tell more -> https://pastebin.com/nGedRU4H - the pass-through device (XCS) was recognized. Both controllers were connected before starting GIMX.
I can capture more with SerialUSB if you want to be sure there is some additional authentication between the controller and XBOX.